November 2, 2011

What's up in networks (2/3): hetnet

Here is the second chapter of the mini-series about some (not-so-fresh) topics in networking area. After openFlow, hetnet.

Hetnet, or the Heterogeneous Cellular Networks:
I am probably not the only one to get bored by GSM cellular networks: they have been created by phone engineers who disliked Internet, they are full of acronyms, they are controlled by an operator, they just works. But cellular networks are now the most common way to access to the Internet. Moreover the devices using these networks are full-featured computers, which are managed by owners who install a lot of applications. The number of devices connected to cellular networks is expected to grow dramatically.

Next-generation cellular networks have good chances to differ from our plain old GSM networks. Here are two technologies that may change the game:
  • femto base stations are small and cheap base stations that anybody can buy and install on its own wired Internet connection (for example here). It means that the clients of a wireless service provider pay (base stations + landline Internet communication + consumed electric power) to improve the infrastructure of the carrier and to have an excellent quality of service at home. Carriers are all jumping into this idea. I still don't understand why would a user prefer to buy a base station and connect to Internet through the 4G although she can use wifi. The main argument is that, wifi wireless spectrum being free and badly managed, a local network can have poor performances because too many wifi access points compete or because too many devices share the pool of wireless channels. The 4G spectrum is licensed and managed by the operator, so some wireless channels can be "reserved" to a user. But if everybody has its own femtocell at home, licensed channels will become scarce too, and nobody will tolerate paying for a femtocell that interfere with the neighbors' ones. In order to tackle this issue, nearby femto base-stations should collaborate to share the wireless spectrum and react to changes in the radio environment (especially when neighbors decide to turn on/off their femto base stations). All scientists interested in peer-to-peer and ad-hoc networks will have fun with the problem of channel allocation: end-users form the infrastructure, ensuring a fair sharing of scarce resources is a challenging objective, clever distributed algorithms should solve the problem, incentives to turn on/off the femtocells should be taken into account. As shown in this article, both deployment and management of femto hetnets are still unclear. Those who are not afraid of acronym orgies can look at these slides for a summary of 3GPP standard and a nice telco-oriented overview of the research problems.
  • direct device-to-device wifi communication is a long-awaited feature. Hurrah, WiFi Direct, which is the official name of this feature in the WiFi alliance, is included in the new Android OS version. At least, wifi direct transmission between devices is becoming a reality, which means that the thousands of academic papers about mesh networks and hybrid ad-hoc cellular networks are suddenly worth reading. However, things have changed. Extending the coverage area of base stations, which has been the most frequent motivation in previous works related to mesh networks, is no longer the main concern of mobile carriers. It is now all about mobile data offloading, that is, avoiding communication via the macro base station. In this context, network operators may combine wifi direct and data caching in devices to reduce the amount of requests sent to the Internet. In other words, strategies related to information-centric networks may turn out to be useful in the wireless world.
In a broader perspective, the over-utilization of wireless networks for accessing the Internet highlights an interesting paradox: the wireless transmission is inherently broadcasting (all devices near the wireless router may hear all messages) although the Internet applications are usually designed for unicast communication (a message has only one destination). The capacity of a mobile carrier to leverage on the broadcasting feature of base stations in their cellular networks may become a key asset.

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